The promise of enabling time and space resolved chemistries has seen the emergence of droplet microfluidics for lab-on-chip technologies. Generally, prior art approaches to transporting droplets have been directed to creating global surface energy gradients by exploiting electrowetting/electrocapillarity, thermo-capillarity, chemistry, or texture. Prior art static global gradients, however, are limited in usefulness because they can only drive droplets over short distances and can never form a closed loop.
Despite recent advances in microfluidic manipulation of droplets, there remains the need for a simple method and apparatus for transporting droplets over a substrate. In particular, there is a need for an apparatus that can transport droplets along complex paths, including, for example, closed loops.